1. Field of the Invention
The present invention relates to a method for manufacturing an optical fiber having desired characteristics over the longer length thereof.
2. Description of the Background Art
For manufacturing an optical fiber preform, there are several methods, such as the Outside Vapor Deposition (OVD) method, the Modified Chemical Vapor Deposition (MCVD) method, the Vapor phase Axial Deposition (VAD) method, and the Rod-in-collapse method. These typical methods for manufacturing an optical fiber preform have been used widely. However, since the allowable scope of the profile shape parameter, compared to that in a ordinary single mode fiber, is limited in a dispersion shifted fiber, a dispersion flatted fiber, and a dispersion compensating fiber, etc., these optical fibers produced by drawing the optical fiber preform made simply by the above-mentioned manufacturing methods have occasionally failed to achieve a target value for their characteristics, such as the chromatic dispersion, the dispersion slope, the polarization dependent loss, and the effective core area.
Therefore, there have been attempts to machine an optical fiber preform so that an optical fiber having the desired characteristics can be produced therefrom. Japanese Patent Application Publication No. 2000-47039 discloses a method in which the core eccentricity of an optical fiber preform and the ovality of the cladding region thereof are decreased by machining the optical fiber preform in the state where the center axis of the core region of the optical fiber preform is set to the center axis of rotation of a cylindrical grinding machine. Also, Japanese Patent Application Publication No. 9-328328 discloses a method in which the unevenness of the surface of an optical fiber preform is decreased by cylindrical grinding performed in the state where the center axis of the core region of the optical fiber preform is set to the axis of rotation of a cylindrical grinding apparatus.
However, the drawback of the conventional methods for manufacturing an optical fiber is that the profile shape parameter changes in the longitudinal direction of the preform according to a slight fluctuation in the manufacturing conditions. That is, as for the above-mentioned kinds of fibers in particular, it was difficult to achieve the desired characteristics uniformly over the entire length of the preform even if a desired profile shape parameter is obtained at one position of the optical fiber preform.